The present invention relates to a method and device for controlling a plurality of relay nozzles in a jet weaving machine. Such relay nozzles are sequentially actuated, i.e. opened, for supporting the insertion of the weft yarn into the shed of the weaving machine, from the insertion side of the machine and up to the arrival end of the shed on the other side of the machine. The actuation of the relay nozlzes is carried out by sequentially opening electro-magnetic or solenoid valves associated with the nozzles. In some known types of weaving machines the relay nozzles are kept open from the moment when they are opened up to the moment when the weft yarn reaches the arrival end of the shed, at which latter moment all relay nozzles are closed simultaneously. In other types of machines the relay nozzles are sequentially closed a predetermined moment of time after they have been opened. The present invention is applicable to both these different kinds of relay nozzle control.
A known method of the above-mentioned kind is for example disclosed in German Offenlegungsschrift No. 28 36 206. There, the relay nozzles are actuated in synchronism with the rotation of the main shaft of the weaving machine. For carrying out this known method, the electro-magnetic or solenoid valves associated with the relay nozzles are connected to and thus receive actuation signals from a rotary sensor in the form of a code disc co-acting with an optical detector, said code disc being fixed on the main shaft.
This known method works in an optimal way only if there is a perfect synchronism between the weft insertion process and the rotation of the main shaft of the weaving machine. However, such a synchronism cannot always be maintained, since on one hand the main shaft rotation is a relatively non-varying parameter in this connection, whereas on the other hand the weft yarn insertion curve as a function of time can vary a great deal in dependence on e.g. the pressure of the utilized compressed medium, preferably air, and also from yarn to yarn having different friction coefficient, thickness and structure. This means with the known method that the control of the nozzles must be carried out with sufficient compensation for the variations in synchronism between the weft insertion process and the main shaft rotation, preferably by providing relatively generous time tolerances for the sequential opening (and closing, if any) of the series of nozzles. As a consequence hereof the nozzles will consume much more pressure medium (air) than would be necessary for the support of weft insertion as such, which altogether means higher production costs for the woven fabric.
The object of the present invention is primarily to provide a method and a device by which the above-mentioned drawbacks have been eliminated.